1. Field of the Invention
The present invention relates to resistance spot welding devices, and more particularly to an electrode system having an improved tip configuration for absorbing a quantity of heat energy.
2. Discussion of Prior Art
Two-component electrode welding devices are used in various industrial applications, including automotive assembly. These devices typically include a conductive shank removably connected to a welding gun, and a conductive welding cap removably connected to the distal end of the shank. As is well known in the art, these devices function to transmit electric currents through adjacently placed subject members, so that the device and members cooperatively generate a quantity of heat energy and a spot weld is produced between the members. During a welding program, the production of heat energy creates a heated zone having initial and final base temperatures, which correlate to the maximum temperature achieved. For example, in a recent study this zone was exemplarily modeled to reflect a spot-weld center temperature of aprx. 1500° C., a 5-cycle temperature of aprx. 400° C. at a radius of 4 mm, and 100° C. at a radius of 8 mm, and a 30-cycle temperature of aprx. 1000° C. for 4 mm radius and 200° C. for 8 mm. The total amount of heat energy produced is proportional to the weld current (i) squared times the total electrical resistance (R) of the parts to be welded times the time (t) that the weld current is on (ΔH=i2×R×t), and typically is aprx. equal to 1 kJ for large-scale programs such as automobile assembly.
The proximity of the welding cap to the heat source results in the transfer of significant amounts of heat energy to the cap and excessive cap temperatures. The resultant heat absorption and excess cap temperatures cause deformation and replacement. Another resultant from the over-heating of caps is the tendency of the cap to “pick-up” material from, or stick to, the subject members. This tendency further causes the cap to change its configuration and reduces its efficiency. Yet another issue associated with the heating of welding caps and their ensuing deformation is the resulting reduced weld nugget diameters and joint tensile strengths.
Conventional cooling systems have been developed to counteract these concerns by increasing the rate of heat energy loss of the cap and, thereby, retarding or reducing the maximum achievable temperature. Where these systems are not properly configured or malfunction, inefficiency concerns arise and, the cooling system may be rendered ineffective. To cure these conditions, the system must be dismantled from the welding device and reconfigured, repaired or replaced. This results in an inconvenience to the worker and down time to the entire process. Even where properly functioning, however, these conventional cooling systems do not eradicate degradation of the welding cap due to heat stresses.
Accordingly, there is a need in the art for an apparatus for and method of more reliably and further reducing the heat absorption and final base temperature of a resistance spot welding cap.